1. Field of the Invention
The present invention relates to a method for jointing cables comprising a cable core constituted by one or more insulated conductors which may be enclosed within an impervious sheath, at least one layer of armouring elements, e.g. wires, surrounding the core and possibly outer corrosion protective means, including conventional steps of jointing the core.
The invention in particular relates to a method for jointing the armouring wires of cables which are subjected to large longitudinal tension during or after installment.
2. Description of the Prior Art
The armouring of cable is designed to satisfy two requirements--protection of the cable core against mechanical external forces acting in a substantially radial direction and protection of the cable core against longitudinal tension.
To provide the necessary protection, band (or tape) type as well as wire type armour are used. Usually the armouring wires or bands are made of steel, e.g. galvanized steel or copper. While the band armouring provides best protection against radial forces, wire armouring is usually provided to take care of longitudinal tension.
When jointing the armouring of cables which are subjected to longitudinal forces to a limited extent, the armouring elements are usually jointed by an ordinary welding or soldering process, the only requirement being that the armour joint should be capable of withstanding radial forces to the same extent as does the armour. According to one method, the armouring elements from the two cable ends are joined with large overlap, the elements from one end being taped or banded onto the core at intervals to provide several slightly extending circular ridges. The elements from the other end are then taped or banded over the first layer, whereby this layer receives a wavy appearance and is locked onto the first layer. This method has, however, several obvious drawbacks.
It is common practice to displace the armour joint relative to the core joint, and when several layers of armour are concerned, to evenly distribute the joints of the various layers over a certain length of the cable.
In connection with cables which are subjected to large longitudinal tension, such as submarine cables which are lowered to the sea bed, it is essential that the armour joint can withstand the tension caused by the weight of the cable.
The problem of obtaining the desired tension resistant joints is strongly pronounced when an installed submarine cable has been damaged and must be repaired at sea.
In order to ensure that the armour joint takes up the desired tension, it is essential that the armour elements take up equal parts of the total tension or, in other words, that the total tension is evenly distributed among the armouring parts.
When circular wire armoured cables are concerned it has been suggested to thread the wire ends and to use a set of tensioning rods to tension each wire individually until they all are considered to have equal tension. When smaller tensions are concerned this method is satisfactory, but it has certain drawbacks when used on cables which are subjected to large tension.
In order to be able to use tensioning rods, the two sets of armouring wires must, when laid back onto the cable core after the core has been jointed, be cut so as to leave a predetermined gap between the wire ends. The ends are then threaded to fit the inside threads of the tensioning rods, whereupon the individual rods are screwed onto the wire ends and tightened. The tightening process causes the tensioning rods to take the same angle of lay as the wires and while the rods should be as long as possible to ensure sufficient tensioning, they should be as short as possible so as not to increase the diameter of the cable excessively. The possibility of damaging the wires at the entrance of the rods is also severe because the wires have to be screwed at an angle into the tensioning rod.